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Potential evapotranspiration and continental drying

Abstract

By various measures (drought area1 and intensity2, climatic aridity index3, and climatic water deficits4), some observational analyses have suggested that much of the Earth’s land has been drying during recent decades, but such drying seems inconsistent with observations of dryland greening and decreasing pan evaporation5. ‘Offline’ analyses of climate-model outputs from anthropogenic climate change (ACC) experiments portend continuation of putative drying through the twenty-first century3,6,7,8,9,10, despite an expected increase in global land precipitation9. A ubiquitous increase in estimates of potential evapotranspiration (PET), driven by atmospheric warming11, underlies the drying trends4,8,9,12, but may be a methodological artefact5. Here we show that the PET estimator commonly used (the Penman–Monteith PET13 for either an open-water surface1,2,6,7,12 or a reference crop3,4,8,9,11) severely overpredicts the changes in non-water-stressed evapotranspiration computed in the climate models themselves in ACC experiments. This overprediction is partially due to neglect of stomatal conductance reductions commonly induced by increasing atmospheric CO2 concentrations in climate models5. Our findings imply that historical and future tendencies towards continental drying, as characterized by offline-computed runoff, as well as other PET-dependent metrics, may be considerably weaker and less extensive than previously thought.

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Figure 1: Changes (future − historical; mm d−1) of ET.
Figure 2: Future versus historical stomatal conductance (m s−1), for the GFDL-ESM2M climate model.
Figure 3: Scatter plot of change in non-water-stressed ET from the GFDL-ESM2M climate model (dNWSET) against change in PET (dPET).
Figure 4: Multi-model median of the relative change (%) of the annual-mean runoff from the historical to the future time period.

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References

  1. Dai, A. Characteristics and trends in various forms of the Palmer Drought Severity Index during 1900–2008. J. Geophys. Res. 116, D12115 (2011).

    Article  Google Scholar 

  2. Sheffield, J., Wood, E. F. & Roderick, M. L. Little change in global drought over the past 60 years. Nature 491, 435–438 (2012).

    Article  CAS  Google Scholar 

  3. Feng, S. & Fu, Q. Expansion of drylands under a warming climate. Atmos. Chem. Phys. 13, 10081–10094 (2013).

    Article  CAS  Google Scholar 

  4. McCabe, G. J. & Wolock, D. M. Increasing Northern Hemisphere water deficit. Climatic Change 132, 237–249 (2015).

    Article  Google Scholar 

  5. Roderick, M. L., Greve, P. & Farquhar, G. D. On the assessment of aridity with changes in atmospheric CO2 . Wat. Resour. Res. 51, 5450–5463 (2015).

    Article  CAS  Google Scholar 

  6. Burke, E. J., Brown, S. J. & Christidis, N. Modeling the evolution of global drought and projections for the twenty-first century with the Hadley Centre climate model. J. Hydrometeor. 7, 1113–1125 (2006).

    Article  Google Scholar 

  7. Dai, A. Increasing drought under global warming in observations and models. Nature Clim. Change 3, 52–58 (2012).

    Article  Google Scholar 

  8. Cook, B. I., Smerdon, J. E., Seager, R. & Coats, S. Global warming and 21st century drying. Clim. Dyn. 43, 2607–2627 (2014).

    Article  Google Scholar 

  9. Fu, Q. & Feng, S. Responses of terrestrial aridity to global warming. J. Geophys. Res. Atmos. 119, 7863–7875 (2014).

    Article  Google Scholar 

  10. Scheff, J. & Frierson, D. M. W. Terrestrial aridity and its response to greenhouse warming across CMIP5 climate models. J. Clim. 28, 5583–5600 (2015).

    Article  Google Scholar 

  11. Scheff, J. & Frierson, D. M. W. Scaling potential evapotranspiration with greenhouse warming. J. Climate 27, 1539–1558 (2014).

    Article  Google Scholar 

  12. Dai, A. Drought under global warming: a review. WIREs Clim. Change 2, 45–65 (2011).

    Article  Google Scholar 

  13. Shuttleworth, W. J. Handbook of Hydrology (ed. Maidment, D. R.) Ch. 4 (McGraw-Hill, 1993).

    Google Scholar 

  14. Shuttleworth, W. J. & Wallace, J. S. Evaporation from sparse crops—an energy combination theory. Q. J. R. Meteorol. Soc. 111, 839–855 (1985).

    Article  Google Scholar 

  15. Budyko, M. I. Climate and Life (Academic, 1974).

    Google Scholar 

  16. Roderick, M. L., Sun, F., Lim, W. H. & Farquhar, G. D. A general framework for understanding the response of the water cycle to global warming over land and ocean. Hydrol. Earth Syst. Sci. 18, 1575–1589 (2014).

    Article  Google Scholar 

  17. Koster, R. D. & Mahanama, S. P. P. Land surface controls on hydroclimatic means and variability. J. Hydrometeor. 13, 1604–1620 (2012).

    Article  Google Scholar 

  18. Schewe, J. et al. Multimodel assessment of water scarcity under climate change. Proc. Natl Acad. Sci. USA 111, 3245–3250 (2014).

    Article  CAS  Google Scholar 

  19. Chiew, F. H. S., Whetton, P. H., McMahon, T. A. & Pittock, A. B. Simulation of the impacts of climate change on runoff and soil moisture in Australian catchments. J. Hydrol. 167, 121–147 (1995).

    Article  Google Scholar 

  20. Milly, P. C. D., Dunne, K. A. & Vecchia, A. V. Global pattern of trends in streamflow and water availability in a changing climate. Nature 438, 347–350 (2005).

    Article  CAS  Google Scholar 

  21. Cook, B. I., Ault, T. R. & Smerdon, J. E. Unprecedented 21st century drought risk in the American Southwest and Central Plains. Sci. Adv. 1, e1400082 (2015).

    Article  Google Scholar 

  22. Sherwood, S. & Fu, Q. A drier future? Science 343, 737–739 (2014).

    Article  CAS  Google Scholar 

  23. Milly, P. C. D. & Dunne, K. A. Macroscale water fluxes 2. Water and energy supply control of their interannual variability. Wat. Resour. Res. 38, 24-1–24-9 (2002).

    Article  Google Scholar 

  24. Allen, R. G., Periera, L. S., Raes, D. & Smith, M. Crop Evapotranspiration—Guidelines for Computing Crop Water Requirements Irrigation and Drainage Paper 56, 15 (Food and Agricultural Organization of the United Nations, 1998).

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Acknowledgements

The World Climate Research Programme’s Working Group on Coupled Modelling is responsible for CMIP; the climate modelling groups listed in Supplementary Table 1 produced, and made available, their model output. For CMIP, the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. A. Berg, S. Kapnick, M. Roderick, J. Scheff and G. Wang gave helpful reviews of our manuscript.

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P.C.D.M. conceived and led the study, interpreted the data and prepared the manuscript. K.A.D. carried out all computations, prepared all figures and assisted with manuscript preparation.

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Correspondence to P. C. D. Milly.

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The authors declare no competing financial interests.

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Milly, P., Dunne, K. Potential evapotranspiration and continental drying. Nature Clim Change 6, 946–949 (2016). https://doi.org/10.1038/nclimate3046

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